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Hi Kingsley,
This is precisely the sort of insight I was looking for when
considering how the requirements and approaches for ontology
re-use might differ between the worlds of semantic tech
applications, linked data and big data. Horses for courses is
exactly right :)
I also just realized I made a mistake - I was confusing owl:sameAs
with owl:equivalentClass. Sorry about that.
So... (responses interleaved)
On 02/02/2014 21:40, Kingsley Idehen wrote:
On
2/2/14 10:11 AM, Mike Bennett wrote:
The problem with using owl:sameAs is that
you have immediately changed the nature of your model: from a
model of concepts to a model of words. That is, from an ontology
to a vocabulary.
Hmm..
When you put Linked Data in the mix its about terms rather than
words i.e., terms being words that have the duality of denotation
and reference baked in. Thus, you can use owl:sameAs to express
coreference in ABox oriented statements about entities.
I find the term "term" a little slippery in its many applications.
Presumably then in Linked Data "term" refers to a label (with a URI)
that denotes an individual in the world or a fact about that
individual? Or does it also refer to TBox assertions about a class
of possible individuals? Elsewhere we tend to use the word "term" in
the latter sense almost exclusively.
So, what does the duality of denotation and reference mean when it
comes to re-using existing ontologies? Are OWL ontologies which have
been optimized for reasoning applications, more or less useful as a
point of reference for linked data? For instance do you find that
those ontologies end up with fewer assertions that can be linked
directly to some ABox term?
For TBox or RBox oriented descriptive statements (for entity types
and relation types, respectively) you have owl:equivalentClass and
owl:equivalentProperty, respectively.
Right - I was thinking of owl:equivalentClass. There's good reason
to use this when asserting that a class in one OWL ontology
represents the same concept as one in someone else's OWL ontology
(though you end up bringing in the assertions from that other
ontology so you'd better be sure it really is the same concept!).
What I was resisting was the tendency to use OWL to make what appear
to be TBox assertions about the existence of a class, where that
class is tied to one natural language word, and another class is
tied to another natural word in the same ontology which is
synonymous, and the synonymy is dealt with using an assertion that
the two classes mean the same thing (have the same extension). When
is that a useful thing to do and when is it the wrong thing to do?
I can see for example that if one were doing text extraction from a
corpus of unstructured data, it would be useful to have an ontology
which defines all the words individually with equivalent class
assertions, whereas if one wanted to reason over concepts (for
example, to calculate financial exposures across financial
instruments and counterparty hierarchies) then you really would not
want to do that.
When you are choosing an ontology to refer to in a linked data
resource, what sort of things do you look for? What makes one
ontology more useful to reference for Linked Data compared to
another? Do these questions even matter?
Horses for courses - so, what would it take to put some useful
language around the parameters of those courses and how to pick the
right horse? That would move things along from the "A is right!"
"No, B is right therefore A is wrong!" type of conversations that we
sometimes see.
Best regards,
Mike
As long as it's clear which one of those you are doing, that's
fine. But I find an ontology of concepts to be far more useful
than a vocabulary of words.
Horse for courses :-)
The only place I would use owl:sameAs is when mapping between
ontologies that have concepts with the same meanings.
See comment above.
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